In the production in series of electrohydraulic automatic transmissions, there occurs within one an the same series of dispersion through different components and parts. This can result in the driving comfort failing differently in two identical automatic transmissions.
Therefore, it is customary in the production in series of such transmissions to test the function upon a testing stand which simulates a vehicle operation, specific rotational speeds and load ratios being simulated by means of driving and driven machines in order then to control a gear change. The gear change is tested in the cycle according to a preset specification with reference to measuring data of input and output rotational speeds and torque sensors. Said test requires the interconnection for the transmission under dry circuit prior to the test proper for ventilating the clutches and pipes so as to obtain a reproducible test run of the power shifts.
To obtain the most uniform possible driving comfort in the different transmissions of a series, it has already been proposed in DE-C 34 36 190 to use in the electronic control of the transmission adaptive functions. This is done by means of a device for electronic control wherein the electrohydraulically actuatable friction elements in the transmission produce the change between the different reduction steps and an actual value that characterizes the shifting operation, specially the grinding time, shifting time, or the rotational speed gradient during the grinding time, is compared with a stored nominal value, a correction value being stored when a presettable divergence is exceeded. This correction value has for the subsequent shifting operations a correcting effect in the sense of the adaptive control upon the formation of a control valve for the friction elements, specially the hydraulic pressure. This device is specially adequate for automatic transmissions which as consequence of a defect have to be changed in a service workshop, a since otherwise the adaptive data stored in the electronic transmission control no longer coincide with the actual mechanical part fo the automatic transmission.
A method for determining characteristic quantities of an electrohydraulically controlled automatic transmission on a testing stand with quick tying of the electronic control has been disclosed in the Applicant's WO 98/17929. Here gear shifts are successively initiated upon a testing stand in the individual reduction steps of the automatic transmission. During the gearshifts a transmission input and a transmission output rotational speed, the same as a transmission input and a transmission output torque and the timed curves thereof are measured. From said measured values are determined as characteristic quantities of the automatic transmission for the clutch to be engaged during the gear change, a filling time, a charge pressure, a reaction time, a frictional value of the disks and a pressure liquid charge. Said characteristic quantities are thereafter stored in a memory so that the electronic transmission control unit can correct, according to said characteristic quantities, the pressure level and the time of the rapid filling pressure of the charge pressure, the same as the pressure level of the shifting pressure.
Hereby the whole tolerance chain can be tested so that control and transmission tolerances be entirely detected. This leads to greater tolerances of the parts and thus to a less costly production. Since the values that characterize the respective transmission are stored in a memory, there is obtained in the electronic transmission control unit, even in case of great divergences between actual and nominal values, a quicker coincidence of the actual and nominal values. But a dry interconnection of the automatic transmission prior to the actual test for ventilating the clutches and pipes is also required here.
The problem on which this invention is based is to provide a method of the kind mentioned above in which, without separate ventilation of the hydraulic components and within a shorter time, the function of the transmission can be tested from the production in series.